1. Field
The following description relates to technology for estimating carrier frequency offset of OFDM signals, and more particularly, to a device and method for estimating carrier frequency is offset of OFDM signals transmitted and received through a plurality of polarized antennas.
2. Description of the Related Art
FIG. 1 is an exemplary diagram illustrating a structure of a polarized antenna transceiver. As illustrated in FIG. 1, multiple polarized waves are simultaneously transmitted and received through a horizontally polarized antenna and a vertically polarized antenna. In FIG. 1, HHH is a channel transfer function between the horizontally polarized antenna of a transmitter and the horizontally polarized antenna of a receiver, HVV is a channel transfer function between the vertically polarized antenna of the transmitter and the vertically polarized antenna of the receiver, HHV is a channel transfer function between the horizontally polarized antenna of the transmitter and the vertically polarized antenna of the receiver, and HVH is a channel transfer function between the vertically polarized antenna of the transmitter and the horizontally polarized antenna of the receiver.
In an ideal environment having no reflected waves, horizontally polarized waves and vertically polarized waves transmitted from the transmitter do not interfere with each other, but in a real-world environment, cross-polarization discrimination (XPD) indicating a degree of interference between two polarized waves has a non-zero value. The XPD is defined as a ratio between two signals when a receiving antenna receives the two signals, one is transmitted in a wave polarized the same as the receiving antenna and the other is transmitted in a wave polarized opposite to the receiving antenna. When the XPD is not zero, it means that the two polarized waves interfere with each other during transmission. This means that the channel transfer functions HVH and HHV have non-zero values in FIG. 1.
Korean Laid-open Patent Application No. 10-2011-0044453 (Apr. 29, 2011) proposes technology that transmits a group of training symbol for each antenna in a non-overlapping manner in order to measure and compensate for the effect of the XPD when OFDM signals are transmitted through the polarized antenna.
FIG. 2 is an exemplary diagram illustrating a configuration of subcarriers of the training symbol for the polarized antenna. When the subcarriers of the training symbols of each polarized wave are arranged as illustrated in FIG. 2, a time domain value of the training symbol of each polarized wave has a repetition feature, and it can be used for carrier frequency synchronization acquisition.
Although the conventional methods can easily obtain carrier frequency synchronization acquisition in each polarized wave when there is no interference between polarized waves, that is, when the XPD value is zero, it is difficult for the conventional methods to obtain carrier frequency synchronization acquisition when there is interference between polarized waves, that is, when the XPD value is non-zero.
Therefore, the inventors studied about technology for accurately estimating carrier frequency offset used for carrier frequency synchronization acquisition when there is interference between polarized waves.